An electrographic printing process wherein a magnetically responsive electrically conductive toner material is deposited directly on a dielectric receiver as a result of electronic current flow from an array of magnetically permeable styli into toner chains formed at the tips of the styli is disclosed in an article entitled "Magnetic Stylus Recording" by A. R. Kotz, Journal of Applied Photographic Engineering 7:44-49 (1981).
The toner material described by Kotz is a single-component, magnetically responsive, electrically conductive toner powder, as distinguished from multiple-component carrier/toner mixtures also used in electrophotographic development systems. The magnetically permeable styli described by Kotz are a linear array of magnetically permeable wires potted in a suitable material and arranged such that the ends of the wires are perpendicular to the receiver surface. The styli serve as recording or transfer electrodes and effect the transfer of toner particles to a receiver. To achieve image-wise transfer of toner each transfer electrode is excited by an independently controllable voltage source through suitable interconnect wiring.
In electrographic printers utilizing a plurality of transfer electrodes, such as printers with wide-format print heads for fast writing speeds or high resolution print heads for high image quality, a large number of transfer electrodes, interconnects, and voltage sources are required. For example, an eight-inch, full-width 300 dot per inch (dpi) electrographic printer requires a print head with 2,400 transfer electrodes and equal numbers of interconnect wires and voltage sources. Such a large number of transfer electrodes makes the print head extremely costly and difficult to manufacture in a compact manner that does not force compromises in system design.
The prior art has not addressed this problem. Tange in U.S. Pat. No. 5,030,974 issued Jul. 9, 1991, describes a plurality of electrode elements for transferring toner to a receiver, but gives no discussion as to how the electrodes are interconnected to voltage sources. In one embodiment Tange discloses that the wires from the transfer electrodes are routed to the lateral edges of the print head. For a large number of electrodes this would require the length of the print head (in the direction of developer flow) to become unacceptably large. Nakayama et al. in U.S. Pat. No. 5,196,890 issued Mar. 23, 1993, describes an electrostatic recording apparatus utilizing a plurality of recording electrodes wherein the interconnecting wires from the print head follow the curvature of the development sleeve and mate to drive electronics which are housed in a protective central section of the apparatus. The protective electronics housing creates a geometrical interference that necessitates a complex developer transport system.
Thus, there is clearly a need for an electrographic print head that incorporates a large number of transfer electrodes and their associated interconnects and drive electronics in a cost-effective, compact, and manufacturable manner that does not force compromises in system design.